A planarization process such as Chemical Mechanical Polishing (CMP) is generally used in semiconductor processes to obtain a relatively planar surface. However, in a case where a material layer is planarized by CMP, it is difficult to control a surface flatness of the material layer after CMP to be in a range of, e.g., several nanometers, if a relatively thick portion thereof is needed to be ground.
On the other hand, if the planarization process is to be performed on a material layer covering features, especially non-uniform features, there is a possibility that the material layer has non-uniformly distributed fluctuations formed thereon due to presence of the features. Thus, the planarization may not be performed consistently.